1. Field of the Invention
The present invention relates to an elastomer molding and in particular to an elastomer molding as a flexible tube for an endoscope.
2. Description of the Related Art
In an endoscope, a flexible elastomer molding is used as a jacket for flexible Lube. Because an endoscope is repeatedly used and should be cleansed and sterilized every time it is used, the jacket for a flexible tube should be impermeable to body fluids, cleaning liquids, antiseptic solutions etc. The jacket for a flexible tube should have such suitable flexibility and elasticity as not to impair insertion into the body cavity.
The conventional jacket for an endoscopic flexible tube has been formed from a mixed resin of a thermoplastic polyester elastomer (TPC) and a thermoplastic polyurethane elastomer (TPU) or a mixed resin of TPU and TPC compounded with soft polyvinyl chloride (PVC).
With recent diversification of sterilization techniques, thermal resistance is also required of the endoscope. However, TPU is inferior to TPC in thermal resistance, and thus TPU is not suitable for use where thermal resistance is required, and TPC is preferably used.
This TPC is composed of a crystallized hard segment functioning as a crosslinking site and an uncrystallized soft segment exhibiting flexibility. TPC comprising polybutylene naphthalate (PBN) as a hard segment is particularly excellent in chemical resistance and also shows autoclave resistance (see, for example, JP-A 2004-141487 [KOKAI]). However, this TPC comprising PBN as a hard segment is rigid with low flexibility attributable to its chemical structure and is thus not suitable for use in the tip of a long endoscope for the large intestine.
On the other hand, TPC comprising polybutylene terephthalate (PBT) as a hard segment has sufficient flexibility for use in the tip of an endoscope. However, TPC comprising PBT has a problem that it is inferior in chemical resistance to TPC comprising PBN and is lacking autoclave resistance.